English

Symmetric Iterations with Countable and $<\kappa$-Support: A Framework for Choiceless ZF Extensions

Logic 2026-01-26 v6

Abstract

We develop a unified framework for iterated symmetric extensions with countable support and, more generally, with <κ<\kappa-support. Set-length iterations are treated uniformly, and when the iteration template is first-order definable over a Godel-Bernays ground with Global Choice, the construction extends to class-length iterations. At limit stages with cf(λ)κ\mathrm{cf}(\lambda)\ge\kappa we use direct limits; when cf(λ)<κ\mathrm{cf}(\lambda)<\kappa we use inverse-limit presentations via trees of conditions together with tuple-stabilizer symmetry filters. The resulting limit filters are normal and κ\kappa-complete, yielding closure of hereditarily symmetric names and preservation of ZF\mathrm{ZF}. Under a κ\kappa-Baire (strategic closure) hypothesis we obtain DC<κDC_{<\kappa}, and under a Localization hypothesis we obtain DCκDC_\kappa. In the countable-support setting we give an ω1\omega_1-length construction adding reals and refuting AC\mathrm{AC} while preserving ZF+DC\mathrm{ZF}+\mathrm{DC}, and we treat mixed products via stable pushforwards and restrictions. For singular κ\kappa, we develop the cf(κ)=ω\mathrm{cf}(\kappa)=\omega case using block-partition stabilizers and trees; for arbitrary singular κ\kappa we introduce game-guided fusion of length cf(κ)\mathrm{cf}(\kappa) and a tree-fusion master condition, obtaining singular-limit completeness, preservation of DC<κDC_{<\kappa}, no collapse of κ\kappa, and no new subsets of any λ<κ\lambda<\kappa.

Keywords

Cite

@article{arxiv.2511.07866,
  title  = {Symmetric Iterations with Countable and $<\kappa$-Support: A Framework for Choiceless ZF Extensions},
  author = {Frank Gilson},
  journal= {arXiv preprint arXiv:2511.07866},
  year   = {2026}
}

Comments

Replaced in the countable case by arXiv:2601.11008, flawed in the uncountable cases

R2 v1 2026-07-01T07:31:17.679Z